1. Field of the Invention
The present invention relates to an inkjet printing apparatus and more particularly to an inkjet printing apparatus in which the contents of an ink tank are stirred.
2. Description of the Related Art
An inkjet printing apparatus may use pigment ink for printing. If the pigment ink is left as it is, pigment ingredients are settled out in an ink tank, resulting in uneven concentration distribution in the ink tank. Printing using the ink tank in which the concentration distribution is uneven may cause unevenness in density in a printed image and hence image quality degradation.
Japanese Patent Laid-Open No. 2010-208151 discloses a technique for a printing apparatus including a sub tank and a main tank, in which the contents of an ink tank filled with pigment ink are stirred at regular intervals. In the printing apparatus disclosed in Japanese Patent Laid-Open No. 2010-208151, the sub tank is provided with an atmosphere communicating passage communicating with the atmosphere, and an air chamber is provided in the atmosphere communicating passage so as to prevent the ink from leaking through the atmosphere communicating passage. In addition, an atmosphere communicating valve is disposed in an opening communicating with the atmosphere in the atmosphere communicating passage. In such a printing apparatus, the atmosphere communicating valve is closed, and an open/close valve in an ink flow path is opened and closed to produce a flow of the ink in the ink tank and the sub tank and thereby stir the ink.
According to Japanese Patent Laid-Open No. 2010-208151, as described above, the flow of the ink in the main tank and the sub tank is utilized to stir the ink in the ink tank, thereby suppressing unevenness in density due to unevenness of concentration distribution in the ink tank.
In the inkjet printing apparatus disclosed in Japanese Patent Laid-Open No. 2010-208151, however, air is always present between the sub tank and the atmosphere communicating valve. Therefore, even if an attempt is made to stir the ink by producing the flow in the main tank and the sub tank by opening and closing the open/close valve, the air between the sub tank and the atmosphere communicating valve acts as a damper to reduce stirring efficiency.
Consequently, there exists a problem of the flow taking place unsuccessfully in the ink tank, resulting in insufficient stirring.